Parameterized queries broken with plv8

Question

I've been trying to get plv8 working on PostgreSQL 10 (completely clean install, never used it before). I've created a function like so:

CREATE OR REPLACE FUNCTION FindActivitiesJS(_id integer)
  RETURNS Text AS
  $BODY$
  var queryResult = plv8.execute('SELECT * FROM activities WHERE activityid = $1', [_id]);
  return JSON.stringify(queryResult);
  $BODY$
  LANGUAGE plv8 VOLATILE;

When I run:

select * from findactivitiesjs(3)

I get:

ERROR: Error: there is no parameter $0 DETAIL: findactivitiesjs() LINE 2: var queryResult = plv8.execute('SELECT * FROM activities WHERE activityid = SQL state: XX000

I've also tried changing the SQL query to SELECT * FROM activities WHERE activityid = $0 but same results. It's something about the parameter on the query, since a SELECT statement with no WHERE clause works fine.

What am doing wrong?